With wet-running pump assemblies, i.e. pump assemblies with electrical drive motors which are designed as canned motors, in which the rotor space is filled with the fluid to be delivered, there exists the danger that the rotor becomes blocked in the bearings given a standstill, due to contamination in the fluid. For this reason, it has been common for some time now, to provide a closure screw at the axial end of the can, said screw being able to be opened, in order with a tool to manually rotate the shaft located in the can and to thus be able to unblock the rotor. The disadvantage with this system however is the fact that the can must be opened, so that fluid can penetrate to the outside out of the inside of the can.
Moreover, it is known to provide a spring-loaded engagement element at the axial end of the can, said element being able to be pressed with a tool from the outside and then coming into engagement with the shaft, in the inside of the can, in order to be able to rotate this shaft for unblocking. In normal operation, the engagement element is held in a manner disengaged from the shaft, by way of spring. The problem with such systems is the fact that the spring can block due to contamination in the fluid, or that the device is not adequately sealed since it breaks through the can, so that fluid can exit to the outside.